2XHDMI Ports can be connected Simultaneously.2XHDMI can be connected to two displays to get 4k UHD Video.But please make sure your all two separately displays are 4k Monitor,and your connected cables to your monitors also are 4k Cable,a originally 4k video source is also needed.If two 4k monitors are connected Simultaneously,only 4k 30hz can be displayed.

(1) Only Use a Thunderbolt 3 port on your Windows system supports MST extend ,Because of the limitations of the system itself, Under Windows system, the 2XHDMI can expand the screen(extend laptop’s image ,display the different Image in 4K external monitors ), but can only output sounds on one device. The audio output device needs to be set up in the ‘control panel’ – ‘sound’ (select the device that needs to be output, and right-click as the default device)

(2) Under Mac OS does not support MST extend ,It can only support mirroring mode, the 2X HDMI Portscan only output the same Image 4K 30HZ(different from the main screen, but the expanded two screens are the same), and the sound can be output from the two devices at the same time.